The proposed cap on short-term rentals in West Marin goes before the California Coastal Commission next week, with the county’s self-imposed deadline for getting new rules on the books fast approaching. If the commission does not endorse the rules promptly, a surge of new rentals is likely to be registered after the county’s moratorium on new S.T.R.s expires on May 23. The regulations emerged after a year of hearings and community meetings that sharply divided…